Lens system



July 10, 1945. R. N. CARTER LENS SYSTEM 2 Sheets-Sheet. 1

Filed Feb. 9. 1942 r W H E W/ n m .A 0 W R W M 500. n

y 0, 1945. R. N. CARTER 2,380,216

LENS SYSTEM Filed Feb. 9, 1942 2 Sheets-Sheet 2 INVENTOR ww i -v ATTYGAG'T.

Patented July 10, 1945 LENS SYSTEM Rolls N. Carter, Rochester, N. Y.. assignor to Eastman Kodak Company, Rochester. N. Y., a corporation of New Jersey Application February 9. 1942, Serial Io. 429,97

'IClalms.

This invention relates to lens systems and has for one incidental object the reduction of depth of field at small apertures to gain artistic effects.

it relates particularly to high aperture objectlves of the type having troublesome internal reilections produced by refracting surfaces on opposite sides of an air space between elements of the system. These reflections cause flare which is particularly noticeable and objectionable at low nperture settings of the lens. I believe that this is due to the diaphragm not cutting down the internal reflections as much as it cuts down the useful light.

The second and main object of the invention is to provide means for cutting down these reflections and the resulting fiare at least as much as it cuts down the useful light To do this I use a filter, preferably one having neutral density, and mounted so as to be positionable alternatively in and out of line with the lens system. Such a filter when in line with the optical system reduces the flare and the useful liaht equally and also permits larger aperture openings at the lower transmission values of the system so as to give a depth of field which is relatively reduced at the low transmission settings of the system. Mountin the filter so that it is operable by the means usually employed solely for adjusting the diaphragm. permits the filter to be automatlcally inserted as the adjusting means is moved to smaller aperture stops. which in this case are calibrated to correspond t0 transmission values rather than actual aperture diameters.

It is the third object of the invention and the most important in practice to cut down the unwanted reflections many times the amount the useful light is cut down. This third object is really an extension of the second object and is accompanied y o ner positioning Of the filter.

According to the invention the filter is 9081- tioned, when axially aligned. in an air space of the lens system which air space is between the particular refrscting surfaces cooperating to cause the troublesome internal reflections. when the filter is thus located. the useful light. i. e.. the light used to form the main imm. Passes through the filter only once and is reduced exnctly by the amount desired. On the other hand, the sun Um light caused by internal reflections passes through this filter at 18.." thi'td times before reaching the image plane and is thus considerabiy reduced relative to the useful lilht in this plane.

Of course. it is not desirable to have the filter permanently in such an air space in the lens since the transmission of the light, at maximum aperture would be reduced and the lens would have a correspondingly reduced speed." Therefore, according to the preferred embodiment of the invention the filter is inserted only at small apertures. Furthermore, it is preferable to have the filter inserted automatically by the diaphragm adjusting means as it is adjusted to smaller stops and to have this filter displaced to one side of the system as the aperture is adjusted to higher stops. In the most preferred form of the invention, the adjusting means which operates both the diaphragm and the filter is arranged to ary the light transmission of the objective by substantially uniform increments but to vary the aperture size non-uniformly so as to compensate for the density of the filter. For examp!e, an M2 lens may have its diaphragm adjusted for controlling the light transmission down to f/5.6 then as the adjusting means is moved so that the scale reads N8, the actual aperture is left unchanged but a filter having a neutral densit of .3 is moved into axial alignment of the system. This filter then remains in place as the diaphragm is reduced further always at a diameter corresponding to one full stop larger than those of the scale reading. A density of .3 reduces the transmission one-half and thus corresponds to a change of one stop such as from f/5.6 to H8.

Other objects and advantages of the invention will be understood from the accompanying drawings in which:

Figs. 1 and 2 are front views of a camera incorporating one embodiment of the invention;

Fig. 3 is a cross section of the lens system incorporatcd in the camera shown in Figs. 1 and 2;

Fig. 4 shows an alternative arrangement to replace the separate diaphragm and filter slide of Figs. 1 to 3:

Fig. 5 is the cross section of a lens system incorporatlng a different embodiment of the invention;

Fil. 6 is a front view of the important details of Pie. B;

Fig. 'l is an expanded perspective of an arrangement alternative to that of Figs. ii and 6;

Figs. 8 and 9 are front views of details of Fig. 7.

In Figs. 1 and 2 a camera II is provided with a lens ll having a variable diaphragm controlled in the usual way by a rim carrying a pointer it. According to the invention. there is also provided adjacent to the diaphragm a slide il having a larto aperture ll therein larger than the maximum ions diameter and a second aperture if with a neutral density thercover. The aperture l2 ma be the same size as the reference aperture ll, but since it is preferably used only at smaller aperture settings, it may be smaller than the aperturq was shown.

The lens system for this camera is made up of four components 20, 2|, 22 and 23 as shown in Fig. 3 which components include refractive surfaces 24 and 25 which cooperate to cause flare. That is, light coming through the lens from, the front strikes the surface 25 and is reflected thereby to the surface 24 wherent it is again reflected through the rest of the lens system to cause flare. At high aperture if controlled by the diaphragm blades 21 this flare producing light is relatively so weak as not to be noticeable or objectionable. However, as the diaphragm closes down to reduce the light transmission of the system, it does not cut down the flare proportionally. This is due to the fact that most of the flare light passes through the paraxiai region of the aperture. According to the invention a filter 29 having neutral density is mounted on a slide 28 so as to be positionable in alignment with the system at low ra-rturos. Such a filter will, of course, act to ri-duee the flare at least linearly proportional to Hureductlon of useful light. For this broad Pui'mpsc it muy be anywhere in alignment with the system and preferably should be inserted instead of changing the aperture.

in a preferred embodiment of the invention, the filter 29 is inserted as shown in an air space Ill the lens system between the retracting surfaces 2' and 25 which cooperate to cause the obivctlonable flare. with this arrangement the ob- )uetionable light must 11338 through the filter at least three times, whereas the useful light passes through it only once. Thus, the flare is reduced many times compared to the reduction in useful light. IL; in the general case, the introduction of this filter may be a substitute for reduction in aperture. The position of the shutter blade N is also indicated in Fig. 3.

One convenient method of having the insertion of the filter corresponding to and replace the change in aperture is shown in Fig. 4. With such an arrangement the usual variable aperture is omitted entirely or is left at maximum opening. As the slide Ill is moved (in place of the slide ii. Figs. 1 and 2) the scale 81 indicates the light transmission of the lens against an index II in terms of the usual aperture stops. For example. apertures ll, If and 8! correspond to aperture steps V2.0. U28 and f/4.0. As the slide is moved so limit the index 18 is opposite f/5.8. the actual aperture H i; no different in size from the aperture II. However. a neutral density filter 3. havinii a density of .3 covers the aperture N and all smaller apertures such as II. Thus, the light transmission of the objective is changed in substiil'ltlillly uniform increments, dividing the transmission by two in each case, but the changes in aperture ize include a break'since there is no change between aperture 8! and H.

Another method of coupling the diaphragm change to the insertion of the filter is shown in Figs, 5 and 6 wherein the diaphragm blades 41 were carried and operated by a member ll which in turn carries an index it to be read against an aperture scal This member ll also carries a cam 42 which. as the diaphragm is adjusted from No.6 to 1/8. engages a cam rider I carrieci on a filter mount l4 pivoted on the point 48. As the member ll is moved to the position 4|, shown in Fig. i]. the filter mount N is mo ed to th osition N against the action of a spring 50 to move a filter 48 from one side of the optical system into axial alignment therewith in the position 08. The position of the shutter blade 48 is also indicated in Fig. 5. In the preferred form of this embodiment. the movement of the diaph agm setting member if from f/5.6 to H8 doe..- nt change the aperture setting, but merely inserts the filter 45 into the system. Similarly. movement of the member Ii from 178 to f/5.G removes the filter.

One method of coupling the filter and diaphragm controls so that they operate alternatively is shown in Figs. 7, 8, and 9. In Fig. 7 the optical system is expanded axially for clarity, the front and rear components 55 and 56 being considerably spaced. A shutter 51 is mounted in front of a diaphragm 58 which is controlled by a gear 58. The position of a filter BI is also controlled by a gear 85. The diaphragm setting means Bl operates two partly mutilated gears and 8! which engage the gears 59 and 55 respectively. When the mutilated portion 62 of the gear 80 is adjacent to the gear 58, the teeth 54 of the gear 63 engage the gear 65. By way of example. the operation starting at maximum aperture will be described. As the aperture setting m'eans Si is moved to smaller apertures, the diaphragm 38 closes down until the mutilated portion 81 comes adjacent to the gear 59 at which time further movement of the member 6i causes no change in aperture. However. at this same time the teeth 84 engage the gear 55 and move the filter 88 from one side of the system into axial alignment with the system. suitable stops. not shown. being provided to insure accurate alignment of the filter.

The filter 88 is carried by lugs 81 on a very narrow rim 68 so that there is minimum interfcrence with the light transmission as the flltei is swung into place. The purpose of this is to prevent undercxposure ii. the operator should accidentaliy happen to set the diaphragm at some point between f/5.6 and US. In fact. since the actual aperture would still correspond to 175.6 and the filter Bil would cover a portion of this aperture, the actual exposure factor would be somewhere between f/5.6 and f/8.

Having thus described the preferred embodiment of my invention. I wish to point. out that it is not limited to the specific arrangement but is of the scope of the appended claims.

What I claim and desire to secure by Letters Patent of the United States is:

1. An objective comprising a lens mount, a highly corrected lens consisting of a plurality of components carried in the mount and having troublesome internal reflections produced cooperatively by retracting surfaces on opposite sides of an airspace between components, and a variable aperture diaphragm for the lens in said airspace. the reflections being relatively more troublesome at small apertures than at large characterized by a zero power light filter of density less than .5 carried by the mount axialiy aligned in said airspace uniformly extending over all of the light beam transmitted by said diaphragm at small apertures only whereby, at said small apertures, the reflection producing light is reduced by at least three passages through the filter.

2. An objective according to claim 1 including means for automatically moving the filter to one side of the light beam at wide aperture settings of the diaphragm,

2,sa0,21o 3 3. An objective comprising a lens mount, a transmission at the lens to correspond to the highly corrected lens consisting 01' a plurality of reading of the index said adjusting means opercomponents carried in the mount and having ating solely on the diaphragm changing its apertroublesome internal reflections produced coopture except between two certain successive stops eratively by refracting surfaces on opposite sides 8 and operating solely on the filters between said of an airspace between components, an adjustacertain stops positioning the filter in said airble diaphragm for the lens between the compospace at the smaller stop setting and out or said nents, and means for adjusting the diaphragm. airspace at the larger stop setting.

characterized by a zero power light filter carried 6. A lens system comprising as its light transby the mount and movable, automatically by the 10 mission control device means for varying the diaphragm adjusting means, to one side of the aperture giving a series 01 successively djfl'erent system at large apertures and into said airspace diameters, two and only two successiveyalues of to extend uniformly over all of the aperture at the diameter being equal, a light flItrTalternasmall aperture settings oi the diaphragm. tively positionable in and out of alignment with 4. An objective comprising a lens mount, a it the system, uniiormiy extending overall 1 th highly corrected lens consisting oi a plurality of light beam transmitted by said ape tm'gwhen in components carried in the mount and having alignment and means including a sca'lfi'tia'librattroublesome internal reflections produced cooped in aperture stops for successively valv s}; the

eratively by retracting surfaces on opposite sides aperture through its larger values d to said of an airspace between components, and an adcertain value, then for moving thi? met r into iustable diaphragm tor the lens between said alignment and then for varying the apbtllure succomponents, characterized by a light filter carcessiveiy through the smaller values and vice ried movably on the mount, and means including versa, the scale readings being calibrated in aca scale marked in aperture stops for adjusting cordance with the transmission ascontmlled both the diaphragm in accordance with the stops exby the aperture and by the nlter,

cept that between two certain successive stops 7. An objective comprising a lens mount, a the aperture diameter remains at substantially highly corrected lens consisting of a plurality of constant value and for moving the filter into said components carried in the mount and having airspace while adjusting irom the larger to the troublesome internal reflections produced coopsmaller of said certain stops and to one side oi eratlvely by retracting surfaces on opposite sides the system while adjusting in the opposite direc- 01' an airspace between components, and a varition between said certain stops. able aperture diaphragm for the lens in said air- 5. Lens diaphragm means for use in a lens sysspace, the reflections being relatively more troutem having troublesome internal reflections problesome at small apertures than at large characduced cooperatively by retracting surfaces on opterized by a filter carried by the mount axially posits sides 01 an airspace between components aligned in said airspace, said filter being posioi the system, said diaphragming means compristioned so that at aperture settings less than a ing a scale marked successively in successive certain small setting, it absorbs the light transaperture stops, an adjustable diaphragm in said mitted by the diaphragm by an amount equivaairspac, a filter alternatively positionable in and lent to a density less than .5 and at maximum out or said airspace and means carrying an index aperture setting, it has no eiiective absorption.

reading on said scale, for adjusting the light ROLLA N. CARTER. 

